Enlarged switch area membrane switch and method

Abstract

A membrane switch (10) is the subject matter of this patent application. The switch (10) includes first and second switch networks connected in parallel to effect a particular function. Spacer bridges (50, 52) are interposed in the first and second switch networks to preclude inadvertent engagement of contacts on lamina surfaces (14, 16, 28, 30). The bridges (50) of the first network are either adjacent or spaced from all bridges (52) of the second network in order to insure that the application of pressure to one of two external laminae (22, 24) will activate at least one of the switch networks.

What is claimed is: 
     
       1. A membrane switch, comprising: (a) A first switch network including: (i) a contact applied to a surface;   (ii) a conductive pad applied to a surface facing said contact surface, said pad being spaced from, but engagable with, said contact along portions thereof to close said first switch network upon application of pressure urging said surfaces toward one another; and   (iii) at least one continuous spacer bridge intermediate said contact surface and said conductive pad surface maintaining said contact and pad spaced from one another; and     (b) a second switch network wired in parallel with, and overlying, said first switch network, said second switch network including; (i) a contact applied to a surface;   (ii) a conductive pad applied to a surface facing said second network contact surface, said second network pad being spaced from, but engagable with, said second network contact along portions thereof to close said second switch network upon application of pressure urging said second network contact surface and said second network conductive pad surface toward one another; and   (iii) at least one continuous spacer bridge intermediate said second switch contact surface and said second switch conductive pad surface maintaining said second network contact and pad spaced from one another, said at least one second network spacer bridge being one of laterally adjacent, spaced, and out of vertical alignment from said at least one first network spacer bridge, wherein there is substantially no vertical overlap of said at least one first network spacer bridge and said at least one second network spacer bridge.     
     
     
       2. A membrane switch, comprising: (a) a central lamina having oppositely facing surfaces and electrical contacts applied to each of said surfaces;   (b) a first external lamina having a surface opposite one of said central lamina surfaces and electrical contacts, engagable with said contacts on said central lamina surface to close a first circuit, applied thereto;   (c) a second external lamina having a surface opposite the other of said central lamina surfaces and electrical contacts, engagable with said contacts on said central lamina surface to close a second circuit wired in parallel with said first circuit, applied thereto;   (d) first and second spacers interposed between said first external lamina and said central lamina, and said second external lamina and said central lamina, respectively, said spacers having overlying windows, having widths, bounding contact engagement areas, formed therein; and   (e) at least one continuous spacer bridge traversing the width of each window, said at least one bridge of one window being one of laterally adjacent, spaced and out of vertical alignment with respect to said at least one bridge of the other window, wherein there is substantially no vertical overlap of said at least one bridge of one window with respect to said at least one bridge of said other window.   
     
     
       3. A switch in accordance with claim 2 wherein said bridges are elongated and parallel with respect to axes of elongation. 
     
     
       4. A switch in accordance with claim 2 or 3 wherein said electrical contacts are applications of silver conductive ink screen printed onto said surfaces of said laminae. 
     
     
       5. A membrane switch, comprising: (a) a first switch network including: (i) a pair of laminae having oppositely facing surfaces and electrical contacts applied to each of said surfaces, said contacts being engagable to close said first switch network upon application of pressure urging said surfaces toward one another; and   (ii) at least one continuous spacer bridge intermediate said first switch network surfaces maintaining said contacts spaced from one another; and     (b) a second switch network wired in parallel with, and overlying, said first switch network, said second switch network including: (i) a pair of laminae having oppositely facing surfaces and electrical contacts applied to each of said surfaces, said contacts being engagable to close said second switch network upon application of pressure urging said surfaces toward one another; and   (ii) at least one continuous spacer bridge intermediate said second switch network surfaces maintaining said contacts spaced from one another, said at least one second switch network spacer bridge being one of laterally adjacent, spaced and out of vertical alignment from said at least one first switch network spacer bridge, wherein there is no vertical overlap of said at least one first switch network spacer bridge with respect to said at least one second switch network spacer bridge.     
     
     
       6. A method of constructing a large area membrane switch, comprising the steps of: (a) overlying one switch network with a similarly sized, second switch network;   (b) supporting laminae of each switch network spaced from a corresponding lamina to preclude inadvertant engagement of contacts screened on facing surfaces of laminae of each switch network, wherein continuous support means of one switch network are misaligned and out of vertical alignment with all continuous support means of the second switch network; and   (c) wiring the two switch networks in parallel.